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Green tea can make blood pressure drugs 'less effective'

It is the healthy choice of many people with high blood pressure. But green tea could actually stop their pills from working properly.

The blood pressure-lowering drug nadolol is less effective after drinking green tea, a study found. The researchers advised those taking nadolol to avoid green tea – and warned that the popular drink may also dilute the effect of some other medicines.

The warning is particularly pertinent to blood pressure patients, as some may switched to green tea in a bid to lower their intake of caffeine. In addition, some studies have credited green tea with lowering blood pressure.

Japanese researchers measured the blood pressure of ten healthy men and women after taking nadolol. They were given the drug twice, once after drinking around two cups of green tea a day for two weeks and again after drinking water. Drinking green tea cut the amount of drug that made its way into the bloodstream by three-quarters.

It also meant that the drug, which is also taken to treat angina and irregular heartbeats and to prevent migraines, was less effective at lowering blood pressure. It is thought that plant chemicals in green tea stop nadolol from being ferried from the gut into the bloodstream, where it can get to work on reducing blood pressure.